You should check out the drop off fees to rent in one country and drop in another. My impression is that could run you hundreds of euros...

It's going to cost you a small fortune to rent a car in Italy and drop it in France.

And even if you do do it, that's an 8-hour drive with no stops, never mind ones in quaint towns. I think you'll HAVE to have an overnight stop.

Why are you thinking of doing this? If the goal is just to get to Paris, why not a flight or the train?

To answer your question, rather than discourage you as I presume you are already aware of the additional costs of a drop off point, there are three possible routes you could take:
Through the Mont Blanc tunnel
Into Switzerland skirting Lake Geneva
Into Switzerland and on to Basel via Lucerne

Each has its attractions.

Mont Blanc – you could visit one of the castles of the Aosta Valley. Would suggest a stop over around Beaune or Dijon in the heart of Burgundy famous for its wines and food.

Via Lake Geneva – enter Switzerland either via the Simplon Pass or the Grand Saint Bernard Pass above Aosta. Again suggest Beaune or Dijon. This is a longer route than the previous one but probably more scenic. It does involve buying a Swiss motorway vignette or sticker. Only problem is that should there be late snows the passes could be closed at least for a few hours.

Via Lucerne – north from Milan you can stop at Lucerne for lunch, exit Switzerland at Basel and suggest a stop over at Colmar. Again you need at Swiss motorway vignette.

I'd also wonder (in addition to other concerns above) where you plan on leaving the car in Paris. Do you realise how difficult and expensive parking is there?